Diseases transmitted by insects (vector borne) account for over 17% of the infectious disease burden globally. Most of these diseases lack efficient mammalian vaccines or treatments, and thus heavily rely on vector control to prevent or reduce transmission. Anopheles and tsetse fly are the two vectors involved in malaria and sleeping sickness transmission, respectively. Current vector control methods largely involve the use of insecticides that are environmentally undesirable, and have diminishing efficacy in light of the emergence of insecticide resistance observed in insects. Understanding the mechanisms that influence vector-parasite transmission biology can help develop new control methods. There is growing evidence that the capacity to transmit parasites (vector competence) is influenced by vector innate immune responses and associations with native microbes. The two disease vectors, mosquitoes and tsetse flies, have varying life histories and different associations with gut microbiota. An important component of the innate immune response to pathogens involves Peptidoglycan Recognition Proteins, PGRPs, which recognize pathogen specific molecules and regulate host immune responses that ultimately clear pathogens. We have identified that the PGRP repertoire and functions in tsetse and mosquito vary in accordance with their different life histories and symbiotic associations. We also found that native microbiota influence vector competence through essential roles they play in host immunity and metabolism. This proposal builds on our preliminary studies and expands our previous findings to: 1) characterize and compare PGRP functions that differ in Anopheles and tsetse focusing on PGRP-LB and PGRP-LD and 2) investigate immune and metabolic contribution of the gut microbiota to vector competence. Implementation of our goals will expand our knowledge on 1) the structure and regulation of PGRPs contributing to vector competence, and 2) influence of metabolic interactions between vectors and microbiota on disease transmission traits. These findings have the potential to advance knowledge on tripartite interactions between vectors, symbionts and parasites, and to develop novel targets for disrupting pathogen transmission.